On-off controlled oil temperature adjusting apparatus with a protective device

ABSTRACT

An on-off controlled oil temperature adjusting apparatus with a protective device comprising a bridge circuit consisting of a heat sensitive portion positioned in oil and a standard heat sensitive portion having one terminal connected to a direct current source and the other terminal connected to a first relay. A second relay with a break contact is inserted in the circuit of said first relay, a series circuit consisting of the break contact of said first relay and a capacitor, a make contact of said first relay connected in parallel with said capacitor, and a make contact of said first relay inserted in a main relay circuit for breaking the power source to the motor for driving a compressor. Said series circuit is inserted in the base circuit of a transistor of the circuit of said second relay.

United States Patent Chigira [54] ON-OFF CONTROLLED OIL TEMPERATURE ADJUSTING APPARATUS WITH A PROTECTIVE DEVICE [72] Inventor: Junii Chigira, Maebashi, Japan [73] Assignee: Kanto Seiki Kabushiki Kaisha,

Maebashi City, Gunna Prefi, Japan [22] Filed: Dec. 4, 1970 [21] Appl. No.: 95,020

[30] Foreign Application Priority Data Dec. 16, 1969 Japan ..44/119808 [52] US. Cl ..62/158, 62/228 [5 1] Int. Cl ..F25b 1/00 [58] Field of Search ..62/158, 209, 228, 229

[5 6] References Cited UNITED STATES PATENTS 3,595,028 7/1971 Schrader ..62/229 [4 1 Aug. 1, 1972 Primary Examiner-Meyer Perlin Att0rneyStevens, Davis, Miller & Mosher 5 7] ABSTRACT An on-ofi controlled oil temperature adjusting apparatus with a protective device comprising a bridge circuit consisting of a heat sensitive portion positioned in oil and a standard heat sensitive portion having one terminal connected to a direct current source and the other terminal connected to a first relay. A second relay with a break contact is inserted in the circuit of said first relay, a series circuit consisting of the break contact of said first relay and a capacitor, a make contact of said first relay connected in parallel with said capacitor, and a make contact of said first relay inserted in a main relay circuit for breaking the power source to the motor for driving a compressor. Said series circuit is inserted in the base circuit of a transistor of the circuit of said second relay.

2 Claims, 1 Drawing Figure This invention relates to an on-off controlled oil temperature adjusting apparatus with a protective device.

Hitherto, it has been proposed to use only on-otf controlled oil temperature adjusting apparatus for oils of machine tools such as hydraulic circuit oil, lubricant, or coolant.

In such apparatus, after the power source to the motor for driving the refrigerating compressor is opened, a large pressure difference remains until the pressures of both the high pressure and low pressure sides of the Freon gas circuit are balanced, so that if the power source is connected again to the motor in order to drive the compressor before both pressures are balanced, a heavy starting current flows through the motor. As a result, the motor is overloaded, becomes overheated and may be burnt out.

In order to avoid the above obstacle, therefore, the switch in the motor power supply circuit must be turned only after a predetermined safety time has elapsed from the instant when the switch is turned off.

An object of the present invention is to provide a protective device for preventing the flow of a heavy starting current through the motor circuit in an on-off controlled oil temperature adjusting apparatus until the pressures of both the high pressure and low pressure sides of the Freon gas compressor are balanced.

According to the present invention, even if the switch in the motor power supply circuit is turned on because the oil temperature has reached a predetermined value, the power source is not connected to the motor until a predetermined time has elapsed and both pressures are balanced.

Other objects and advantages of this invention will further become apparent from the following explanation referring to the drawing. Said drawing is a schematic view of an on-off controlled oil temperature adjustin g apparatus according to this invention.

In the device of this invention, as shown in the drawing, a bridge circuit consisting of a heat sensitive portion or thermistor l, a standard heat sensitive portion or thermistor 2 and resistors 12 and 13 is connected to a direct current power source B. A relay 4 is connected to a break contact 5 associated with a relay 3. A series circuit consisting of a break contact 6 of the relay 4 and a capacitor 8 ,is inserted in the base circuit of a transistor 14 the relay being connected in series with the collector of transistor 14. A make contact 7 of the relay 4 is connected in parallel with the capacitor 8 and.

a make contact 9 of the relay 4 is inserted in a circuit of a main relay for breaking and making the power source to a motor 10 for driving a compressor 11. The heat sensitive portion 1 is positioned in the oil for a machine tool 23 and said is located standard heat sensibecause the oil is cooled to a predetermined temperature by a refrigerating machine, the output voltage of the bridge circuit comprising the heat sensitive portions 1 and 2 and resistors 12 and 13 becomes lower than a predetermined value. Thus, the current flowing through the relay 4 decreases, contact 6 is closed and contacts 7 and 9 are opened by the deenergization of relay 4. The current flowing through the motor 10 is broken by the deenergization of the main relay 15, so that operation of the refrigerating machine is stopped.

The relay 3, on the other hand, is energized from the instant that the contact 6 is closed until capacitor 8 is fully charged and therefore contact 5 remains open.

Thus, relay 4 is not energized and the compressor 11 is not driven even if the output voltage of the bridge circuit comprising the heat sensitive portions 1 and 2 and resistors 12 and 13 reaches a value which would operate relay 4.

The relay 4, however, is energized when capacitor 8 is fully charged and the compressor 1 l is driven.

It is preferable that the capacity of the capacitor 8 be of such value that the duration of time required for charging the capacitor 8 is equal to or over the time necessary to balance the pressures of both the high pressure and low pressure sides of the compressor.

As. mentioned above, according to the protective device of this invention, the power source is not applied to the motor until the time necessary to charge the capacitor has elapsed, even if the heat sensitive circuit is operated because the oil temperature is elevated and the temperature difference between the oil and the room exceeds a predetermined value Y after the motor was stopped because the difference between the oil temperature and standard temperature became less than the predetermined value X.

and the room becomes lower a predetermined value X Accordingly, the power source is not connected to the motor prior to the time when the pressures of the high pressure and low pressure sides of both the Freon gas compressor are balanced.

What I claim is:

I. An on-off controlled oil temperature adjusting apparatus with a protective device comprising a. a bridge circuit including a heat sensitive portion (1) for positioning in the oil of a machine tool and a standard heat sensitive portion (2);

b. a first relay (4) having a break contact (6) and first and second make contacts (7) and (9),

c. a second relay (3) having a break contact (5), said break contact (5) being connected in series with said first relay (4),

d. a transistor (14) having its collector-emitter circuit connected in series with said relay (3),

e. coupling means connecting said series-connected first relay (4) and break contact (5) and said series-connected transistor (14) and relay (3) across said bridge circuit,

f. a capacitor (8) connected in series with the break contact (6) of said first relay (4) between the base of said transistor (14) and said coupling means, the first make contact (7) of said relay 4) being connected in parallel with said capacitor (8).

g. a refrigerating machine (16 19) having a compressor (1 l) for cooling said oil, and

h. a motor (10) for driving said compressor (11),

- said motor being coupled to a power source by the second make contact (9) of said first relay (4).

2. Apparatus as defined by claim 1 wherein said heat sensitive portions (1) and (2) are thermistors. 

1. An on-off controlled oil temperature adjusting apparatus with a protective device comprising a. a bridge circuit including a heat sensitive portion (1) for positioning in the oil of a machine tool and a standard heat sensitive portion (2); b. a first relay (4) having a break contact (6) and first and second make contacts (7) and (9), c. a second relay (3) having a break contact (5), said break contact (5) being connected in series with said first relay (4), d. a transistor (14) having its collector-emitter circuit connected in series with said relay (3), e. coupling means connecting said series-connected first relay (4) and break contact (5) and said series-connected transistor (14) and relay (3) across said bridge circuit, f. a capacitor (8) connected in series with the break contact (6) of said first relay (4) between the base of said transistor (14) and said coupling means, the first make contact (7) of said relay (4) being connected in parallel with said capacitor (8). g. a refrigerating machine (16 - 19) having a compressor (11) for cooling said oil, and h. a motor (10) for driving said compressor (11), said motor being coupled to a power source by the second make contact (9) of said first relay (4).
 2. Apparatus as defined by claim 1 wherein said heat sensitive portions (1) and (2) are thermistors. 